Coagulation Abnormalities Made Easy

Back decades ago, the coagulation cascade was taught in terms of 2 pathways, the intrinsic versus the extrinsic. Figure 1 shows a very simplified version of the proposed waterfall/ cascade model of the coagulation system. Unfortunately, as we started to understand more about the coagulation system, it became more and more complex. Many of the enzymes were found to be cofactors or were precursors to the active form. We also found that the 2 pathways were not completely separate in function. They appeared to be an intertwined system where modulation of one arm may or may not affect the second arm. The modern view of coagulation is to actually look at the coagulation system as a series of steps, 1) initiation, 2) amplification, and 3) propagation, as opposed to distinct pathways, (1) but the old 2 pathway model is still beneficial in terms of helping us understand what abnormal coagulation tests mean. This chapter will exam some causes of abnormal coagulation in the perioperative period and discuss agents that are used to modulate the coagulation system.